The abovementioned parking mechanism is adapted to engage a gear member secured to the output shaft of the transmission with a pawl member pivotally supported on the transmission case to fix the output shaft to the transmission case when the vehicle is parked.
When a manual valve within the hydraulic control apparatus of an automatic transmission is shifted from reverse (R) to parking (P), the oil line communicating with the manual valve is changed over and a drain oil line is opened to discharge the pressurized oil that establishes the R range (see the specification of Japanese Patent Kokai No. 58-30566). In the conventional drain oil line, this discharge of pressurized oil is performed in rapid fashion.